This invention relates to ultrasound imaging of a subject under study, and more particularly relates to the simultaneous display of B-mode and Doppler flow information.
In state-of-the-art multi-mode ultrasound scanners, a pulsed Doppler sample gate (or range gate) can be manually positioned via trackball control over the vessel of interest in the B-mode image. For each Doppler transmit firing, a segment of the received Doppler signal is passed through a xe2x80x9csum and dumpxe2x80x9d operation which produces one Doppler signal sample corresponding to the desired sample volume. Doppler samples extracted from many transmit firings over an analysis time interval (typically 10 ms) are used to compute a Doppler frequency spectrum via standard Fast Fourier Transform (FFT) spectral analysis. The resultant xe2x80x9cinstantaneousxe2x80x9d Doppler spectrum constitutes one vertical line in the frequency versus time spectrogram display, in which the intensity (or color) is modulated by the spectral magnitude. The Doppler frequency shift fd, is often converted into flow velocity (speed) v, based on the Doppler equation: v=cfd/(2fo cos xcex8), where fo is the transmit frequency, and xcex8 is the Doppler angle, or angle between the ultrasound beam and the velocity vector.
The advantage of the conventional spectral Doppler technique described above is that it provides a continuous display of the Doppler spectral distribution as it evolves over the cardiac cycle, from which many diagnostic waveform indices such as the systolic-to-diastolic ratio, are derived. The limitation is that only the Doppler frequency distribution within a single sample volume can be measured. It is not possible to simultaneously observe how the flow velocities are changing in two or more sample volumes across the vessel diameter.
Tortoli et al. taught in (xe2x80x9cSpectral velocity profiles for detailed ultrasound flow analysisxe2x80x9d IEEE Trans. UFFC, vol. 43, pp. 654-659, 1996) the operation of a multi-gate Doppler system for measuring the time-varying flow velocity profiles along a Doppler beam. The system is capable of computing in real-time the FFT of Doppler signals detected from 64 equally spaced range gates. The resultant data is displayed in a range versus velocity/frequency format where the gray scale intensity is modulated by spectral power. These spectral Doppler profiles provide a direct and intuitive representation of the pulsatile flow velocity profile across the blood vessel. However, no background tissue anatomical data is available.
Today""s premium ultrasound scanners are generally capable of simultaneous acquisition of single-range-gate spectral Doppler and B-mode data. To maximize frame rate, usually a part or entire frame of B-vectors are interleaved with the Doppler firings. If Doppler needs to be suspended during the B-mode interval in order to maintain an acceptable B-mode frame rate, a time gap will occur in the Doppler data and is usually filled in with synthesized Doppler data.
A scanner which can acquire, process and display B-mode and multi-gate spectral Doppler flow images simultaneously would clearly provide a new useful tool for vascular diagnosis. It will be especially interesting to be able to monitor the flow profile changes in conjunction with vessel wall movements over the cardiac cycle.
The preferred embodiments are useful in an ultrasound system for acquiring and displaying Doppler and B-mode data from a subject under study. In such an environment, ultrasound waves are transmitted into the subject under study, preferably by an ultrasound transmitter. Backscattered signals are generated in response to the ultrasound waves backscattered from the subject under study, preferably by a receiver.
A plurality of Doppler signal samples representing different depth increments within the subject are generated, preferably by a plurality of range gates responsive to the backscattered signals. A plurality of Doppler frequency signals representing the different depth increments are generated in response to the Doppler signal samples, preferably by a logic unit. B-mode data is generated in response to the backscattered signals, preferably by the logic unit. A B-mode image is displayed in response to the B-mode data and a Doppler image is displayed representing the Doppler frequency along a first axis and representing the depth increments along a second axis in response to the Doppler frequency signals.
By using the foregoing techniques, B-mode and Doppler information can be displayed in a manner which facilitates interpretation and diagnosis by ultrasound users.